Surgical access and nerve surveillance

ABSTRACT

An expandable tip cannula system, comprising: a hollow cannula shaft having a proximal end and a distal end; and an expandable tip mounted at the distal end of the hollow cannula shaft, the expandable tip comprising a plurality of generally-triangular shaped petals held together in a radially-inwardly tapered arrangement between adjacent petals, each petal comprising a nerve sensing electrode disposed therein.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/494,908, filed Jun. 6, 2012 (now issued as U.S. Pat. No. 8,489,170), whichis a continuation of U.S. application Ser. No. 11/489,020, filed Jul.18, 2006 (now abandoned), which is a divisional of U.S. application Ser.No. 10/431,619, filed May 7, 2003 (now issued as U.S. Pat. No.7,079,883), which is a divisional of U.S. patent application Ser. No.09/325,998, filed Jun. 4, 1999 (now issued as U.S. Pat. No. 6,564,078),which claims benefit under 35 U.S.C. §119(e) from U.S. ProvisionalPatent Application Ser. No. 60/113,651 filed Dec. 23, 1998; U.S.Provisional Patent Application Ser. No. 60/120,663 filed Feb. 19, 1999;and U.S. Provisional Patent Application Ser. No. 60/123,268 filed Mar.8, 1999; the complete disclosures of which are hereby incorporatedherein by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to nerve surveillance systems and tocannulae systems for use in minimally invasive spinal surgery.

II. Discussion of the Prior Art

A significant danger of performing intervertebral operations oraccessing an intervertebral space during spine surgery is that ofinadvertently contacting or damaging the para-spinal nerves, includingthe exiting nerve roots, traversing nerves and the nerves of the caudaequina. The exact location of these para-spinal nerves cannot bedetermined prior to the commencement of surgery. Moreover,intervertebral spaces in the spine have other sensitive nerves disposedat locations which are not entirely predictable prior to insertion ofthe surgical tool into the intervertebral area. Accordingly, the dangerof pinching or damaging spinal nerves when accessing an intervertebralspace has proven to be quite limiting to the methods and devices usedduring minimally invasive spinal surgery. In addition, as cannulae arereceived through the patient's back, such as when performing minimallyinvasive spinal surgery, minor blood vessels are ruptured, therebyblocking the surgeon's vision inside the intervertebral region after thecannula has been inserted.

SUMMARY OF THE INVENTION

The present invention provides nerve surveillance probes which areadapted to assist the surgeon in identifying the presence and locationof para-spinal nerves as the probe is advanced during minimally-invasivesurgery, thus providing a device for guiding the path of other surgicalinstruments to be inserted into this intervertebral space. In apreferred aspect of the present invention, an expandable tip cannulasystem is provided which functions both as an access portal for spinalsurgery and as a system for nerve surveillance such that the presenceand relative position of para-spinal nerves can be detected as theexpandable tip cannula is inserted through the patient's facia andpara-spinal musculature. An advantage of determining the position of thepara-spinal nerve with respect to the distal tip of the cannula inparticular is that the para-spinal nerve can be avoided or gently movedout of the surgeon's way while inserting the cannula. Accordingly, in apreferred aspect, the present invention provides a cannulated systemwhich is adapted to assist the surgeon in guiding the path of surgicalinstruments received into the intervertebral space, while identifyingthe presence and location of para-spinal nerves as the cannula isadvanced to a patient's intervertebral space during minimally invasivesurgery.

Optionally, the present nerve surveillance expandable tip cannula mayalso be adapted to selectively electrically induce cauterization ofsevered blood vessels when the cannula or other surgical instrumentssever small blood vessels when they are inserted percutaneously into thepatient and are advanced along a path into the patient's intervertebralspace. An additional advantage of the present cannula system thereforeis that, prior to piercing the annulus of an intervertebral disc,vessels on the surface of the disc may be cauterized to assure clearvision inside the disc after surgical entry is made.

In one embodiment, the present expandable tip nerve surveillance cannulapreferably comprises a hollow tubular body with an expandable tipportion mounted at its distal end. In a preferred aspect of theinvention, the expandable tip portion comprises a plurality of generallytriangular shaped petals which are held together in a radially-inwardlytapering arrangement by breakable seals disposed between adjacentpetals. Since the expandable tip portion of the cannula tapers to anarrow blunt end, the cannula can be easily pushed through the patient'sfacia and spinal musculature using blunt dissection, while minimizingthe amount of cutting and tearing of such structures.

Alternatively, a central electrode can be disposed on a centralobturator passing though the cannula and a second electrode can bedisposed on a distal end of a second cannula, wherein the second cannulais used to open the petals.

An obturator shaft which is slidably received within the hollow tubularcannula body provides support for the cannula, giving the cannulasufficient strength such that the cannula can be inserted percutaneouslythrough the patient's facia and para-spinal musculature. Preferably, theobturator has a large solid handle which allows the surgeon to grasp andpush the cannula through the resistance of the facia and para-spinalmusculature.

After the cannula has been inserted and is resting on the patient'sannulus, an inner cannula or rod which is slidably received within thecannula is then used to separate the breakable seals, opening the petalsradially outwards to a distance sufficient to provide access forsurgical instruments passing therethrough.

In some preferred aspects, an electrode is disposed in each of thepetals, and most preferably at or near the distal end of each of thepetals. In other aspects of the invention, a plurality of electrodes areradially disposed about the distal end of the obturator and theelectrodes protrude out of a small hole defined by truncated petals, aswill be explained.

In various aspects of the present invention, the electrodes can bepowered at a low level to thereby sense the position of a para-spinalnerve through continuous real time electromyographic monitoring, oralternatively, the electrodes can be powered at a higher level such thatthey operate to cauterize blood vessels. Safety systems ensure thatpower levels sufficient to cause cauterization are not activated if anerve is sensed to be near the electrodes at the distal end of thecannula.

In alternate embodiments, the present invention comprises an elongatednerve surveillance probe having one or more electrodes at its distaltip. In such aspects, the nerve surveillance probe is preferablyadvanced to the patient's intervertebral space through a cannula. Inother alternate embodiments, the present nerve surveillance probe isreceived into the patient through various cannulae and expandable meshtrocars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a first nerve surveillance probe ofthe present invention.

FIG. 2 is a sectional side elevation view of the first nervesurveillance probe positioned adjacent the spinal nerve with the firstprobe received within a first cannula which is itself received with anexpandable mesh.

FIG. 3 shows the probe of FIG. 2, but with the mesh expanded and asecond cannula received thereover, (after the distal ends of the firstcannula and expandable mesh have been advanced past the nerve).

FIG. 4 is a sectional side elevation corresponding to FIG. 3, but withthe first probe and first cannula removed.

FIG. 5 is an end view corresponding to FIG. 4.

FIG. 6 is a side perspective view of a second nerve surveillance probeof the present invention.

FIG. 7 is a sectional side elevation view of a second nerve surveillanceprobe received within the second cannula.

FIG. 8 is an end view corresponding to FIG. 7.

FIGS. 9A, 9B and 9C sequentially show a schematic view of an expandablemesh system as moved from a contracted position (FIG. 9A) to an expandedposition (FIG. 9B), and with an outer cannula received thereover (FIG.9C).

FIG. 10 is an end view of the nerve surveillance probe of FIG. 6 pushinga nerve out of the way of an advancing cannula.

FIG. 11 is an illustration of an expandable tip nerve surveillance probeof the present invention.

FIG. 12 is a perspective distal view of the system of FIG. 11.

FIG. 13 is a view of the distal tip of the system of FIG. 12, with thepetals in a closed position.

FIG. 14 is a view corresponding to FIG. 13, but with petals in an openposition.

FIG. 15 is a sectional view of the system of FIG. 11, with an obturatorreceived therein and the petals in a closed position.

FIG. 16 is a schematic illustration of the electrodes at the distal tipof the present invention, the electrodes being used to sense theposition of a para-spinal nerve.

FIG. 17 is a sectional view of the system of FIG. 11 with an innercannula received therein and the petals in an open position.

FIG. 18 is a side view of an alternate embodiment of the distal tipregion of the present invention having truncated petals.

FIG. 19 is an end view corresponding to FIG. 18.

FIG. 20 is a top plan view of a peel back expandable tip cannula.

FIG. 21 is a side elevation view of the peel back cannula FIG. 20.

FIG. 22 is a side sectional view of the peel back cannula of FIG. 20 ina sealed position.

FIG. 23 is a sectional side elevation view of the peel back cannula ofFIG. 20 in an open position.

FIG. 24 is a top plan view corresponding to FIG. 23.

FIG. 25 is a side elevation view of a curved petal nerve surveillanceprobe.

FIG. 26 is a side elevation view corresponding to FIG. 25, but with thepetals in an open position.

FIG. 27 is a view corresponding to FIG. 26, but with an expandableelastomer shown wrapped around the distal end of the curved petals.

FIG. 28 is a sectional elevation view of the distal end of an alternatenerve surveillance cannula.

FIG. 29 is a perspective view of an alternate nerve surveillance probe.

FIG. 30 shows the surveillance probe of FIG. 29 with the petals openedby an inner cannula.

FIG. 31 corresponds to FIG. 30, but with the internal obturator removed.

FIG. 32 corresponds to FIG. 30, but with the internal obturator advanceddistally.

FIG. 33 corresponds to FIG. 31, but with the internal cannula advanceddistally.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As will be set forth herein, the present invention encompasses bothnerve surveillance probes which are received through cannulae, andvarious expandable tip cannulae comprising nerve surveillance probes attheir distal ends.

In a first preferred embodiment, as is seen in FIG. 1, anelectromyography nerve surveillance probe 10 having a blunt end 11 isprovided. Electrode 13 is disposed at the distal end of probe 10 and ischarged by electrical contacts 15. As electrode 13 approaches nerve 20(as seen in FIG. 2), the minimal threshold depolarization value elicitedby the electrode will result in corresponding electromyography activity,such that the presence of nerve 20 can be sensed by standardelectromyographic techniques, thus indicating the presence of the nerve.Specifically, using standard electromyographic techniques, the presenceof nerve 20 will be sensed by appropriate needles or patches attached tothe appropriate muscle as electrode 13 stimulates, and therebydepolarizes nerve 20.

In an exemplary method of application, (as is shown in FIG. 2), thepresent nerve surveillance probe 10 can be advanced percutaneouslythrough the patient's back in a posterolateral approach towards thepatient's intervertebral space using the arrangement in which a firstcannula 30 surrounds probe 10 as the probe is advanced. As probe 10 isadvanced, it will then become positioned proximal nerve 20. When thisoccurs, the presence of nerve 20 relative to probe 10 will be determinedby the signal generated by electrode 13 as set forth above.

In one preferred aspect of the present invention, an expandable mesh 32is received over first cannula 30 such that expansion of this mesh fromthe contracted position shown in FIG. 2 to the expanded position shownin FIG. 3 will gently move nerve 20 out of the way.

Also in a preferred aspect as shown in FIG. 3, a second cannula 34 canthereafter be received over expanded mesh 32, thereby providing a largepassageway 38 for intervertebral access when probe 10, first cannula 30,and expanded mesh 32 are removed as shown in FIGS. 4 and 5. Accordingly,the large passageway 38 into the intervertebral area provided by cannula34 protects sensitive nerve 20 while providing access for surgicalinstruments therethrough, including such surgical instruments asintervertebral inserts, bone decorticators, cameras, articulatingforceps, intervertebral inserts and intervertebral positioning systems.

As is seen in FIG. 6, a second nerve surveillance probe 9 is alsoprovided. Nerve surveillance probe 9 has a plurality of electrodes 12,14, 16 and 18 disposed at radial locations adjacent to blunt distal end8, as is seen in FIGS. 6, 7 and 8. Radially disposed electrodes 12, 14,16, and 18 perform a variety of useful functions, as follows.

Referring to FIG. 8, as electrodes 12, 14, 16, and 18 are disposed atradial locations around the tip of probe 10, the electrodes which areclosest to nerve 20, (in this case electrode 14, and to a lesser degreeelectrodes 12 and 16), will operate to depolarize the nerve such thatthe presence of nerve 20 can be detected by standard electromyographictechniques. As such, a signal will be generated telling the operatingsurgeon that nerve 20 is proximal to electrode 14. As can beappreciated, should nerve 20 instead be positioned in anotherorientation, the signal from electrodes 12, 14, 16 and 18 would insteadindicate the presence of the nerve at a different location. Accordingly,probe 9 can be operated as a tool for inspecting the interior passagewayof cannula 34 to determine if nerve 20 had become inadvertently trappedtherein as cannulae 34 is advanced over expanded mesh 32. Moreover, asthe electrodes 12, 14, 16, and 18 are disposed at radial locationsaround the distal end of the probe, it is possible to determine theexact location of nerve 20. Preferably as well, each of electrodes 12,14, 16, and 18 will be activated in a repeating sequence with asufficient delay time therebetween to detect an electromyographicresponse.

In another aspect of the invention, radially disposed electrodes 12, 14,16, and 18 can be used for electrocoagulation of blood vessels, forexample, blood vessels on the patient's annulus when accessing thepatient's intervertebral region. Specifically, as a plurality ofelectrodes are disposed at the distal end of probe 9, it is possible topass current between various electrodes, thus cauterizing adjacent bloodvessels.

In another aspect of the invention, radially disposed electrodes 12, 14,16, and 18 can be used to assist in avoiding, or alternatively inmoving, nerve 20 as follows. Referring to FIG. 10, nerve 20 will bedetermined to be adjacent to electrode 14 using the above set forthmethod. Probe 10 can then be gently moved in a radial direction awayfrom electrode 14, as is shown by arrow D, such that nerve 20 can thenbe gently pushed out of the way, providing safe access to the patient'sintervertebral space. Alternatively, the movement of probe 10 in adirection opposite direction D will push the nerve out of the way suchthat a cannula can then be advanced past nerve 20 without damaging thenerve.

In another aspect of the present invention as shown in FIGS. 9A, 9B and9C, the expansion of mesh 32 is controlled as follows. As is shown inFIG. 9A, expandable mesh 32 is in a contracted position and is mountedon the end of a cannula 35. A distal end of mesh 32 is positionedagainst the patient's annulus 40 or any other suitably hard bonestructure. Pushing rod or cannula 35 in direction D2 will compress mesh32, causing it to expand radially and shorten. This movement willdisplace nerve 20 (shown here in cross section). Following this, cannula37 can be slid over expanded mesh 32 is seen in FIG. 9B. Following this,cannula 37 can be advanced past nerve 20, gently pushing nerve 20 stillfurther out of the way, as shown in FIG. 9C. Lastly, rod or cannula 35and attached mesh 32 can be removed, leaving a large cannulatedpassageway to the annulus or intervertebral space.

It is to be understood that the present nerve surveillance probes can beused without the expandable mesh system of FIGS. 9A, 9B and 9C.Moreover, it is to be understood that the present method and apparatusof minimally invasive nerve surveillance can be used in any arthroscopicprocedure.

As can also be appreciated the present nerve surveillance probes areable to detect the presence of any other efferent skeletal motor nervein addition to the spinal nerve and can thus be used in various surgicalprocedures. Alternatively, using evoked potential electromyography, thepresent nerve surveillance probes are also adapted to sense the presenceof afferent sensory nerves in response to signals received in the spinalcord or cerebral cortex.

In a second preferred embodiment, the present invention provides anexpandable tip nerve surveillance cannula system 110 comprising anendoscopic hollow cannula shaft 112 having an expandable tip 113comprised of a plurality of petals 114 (the details of petals 114 arebetter shown in FIGS. 12, 13, and 14). System 110 further comprises anobturator 120 which is slidably received within cannula shaft 112. As isshown in FIG. 15, obturator 120 is a rigid structure which providesinternal support to cannula shaft 112 such that cannula shaft 112 can bereceived percutaneously. Shaft 112 can have a cross section which iscircular, oval, racetrack-shaped or any other design. By holdingobturator handle 122, the surgeon is able to advance cannula shaft 112through the patient's para-spinal musculature and dock expandable tip113 at the patient's annulus.

As seen in FIGS. 12 and 13, expandable tip 113 is comprised of aplurality of petals 114, held together by breakable seals 115. Breakableseals 115 can be formed by an elastomeric material with predictablefailure segments between the petals. In one preferred aspect each ofpetals 114 has an electrode 116 disposed therein as shown. Electrodes116 serve the following important functions.

First, electrodes 116 can be used for electromyography, and inparticular to sense the presence and relative position of para-spinalnerves as cannula shaft 112 is advanced. Referring to FIG. 16, as can beseen electrodes 116 a, 116 b, 116 c, 116 d, 116 e and 116 f are disposedradially about cannula shaft 112, with one electrode disposed in each ofpetals 114, as has been described. Electrodes 116 a, 116 b, 116 c, 116d, 116 e and 116 f assist in sensing the presence and location ofpara-spinal nerve 160 as follows. The electrodes closest to nerve 160(in this case electrodes 116 b and 116 c, and to a lesser degree,electrodes 116 a and 116 d) will operate to depolarize nerve 160 suchthat the presence of nerve 160 can be detected by electromyography. Assuch, shaft 112 can be moved in direction D, thereby avoiding nerve 160as shaft 112 is inserted. Alternatively, of course, shaft 112 can bemoved in the opposite direction to D, such that cannula shaft 112 gentlymoves nerve 160 out of the way. Moreover, when none of electrodes 116 a,116 b, 116 c, 116 d, 116 e and 116 f sufficiently stimulate todepolarize the nerve, and thereby assist in its detection, shaft 112 canbe safely advanced toward the patient's intervertebral space. Shouldeach one of electrodes 116 a, 116 b, 116 c, 116 d, 116 e and 116 fdepolarize the nerve, this would indicate that the nerve is directly infront of the advancing cannula shaft 112. Accordingly, the cannula shaftcould be moved such that contact with the nerve is avoided.

Alternatively, when none of electrodes 116 a, 116 b, 116 c, 116 d, 116 eand 116 f indicate the presence of a nerve, electrodes 116 a, 116 b, 116c, 116 d, 116 e and 116 f can be powered to a higher level such that acauterization of minor blood vessels can be achieved by passingincreased electric current between each of the various adjacentelectrodes, thus cauterizing adjacent blood vessels. Preferably, thepresent invention comprises a safety system such that cauterizationpower levels for electrodes 116 are not activated when any of electrodes116 sense the presence of a para-spinal nerve thereby.

Preferably, each of electrodes 116 a, 116 b, 116 c, 116 d, 116 e and 116f are operated in sequence, affording a sufficient latency periodtherebetween for the detection of an electromyographic signal.

As seen in FIG. 11, button 121 can be used to activate the blood vesselcauterization functions. Buttons 121 and 123 are conveniently located onthe near handle 122 such that they may be activated while the surgeongrips obturator handle 122.

Subsequent to being positioned at the patient's annulus, obturator 120is removed from cannula shaft 112. As seen in FIG. 17, inner cannula 130is then inserted into cannula shaft 112. Inner cannula 130 is theninserted into cannula shaft 112. Inner cannula 130 is dimensioned to beof a size that, when fully inserted into shaft 112, inner cannula 130breaks apart seals 115, forcing petals 114 to be displaced radiallyoutwards to a distance of at least the internal diameter of shaft 112 asshown. Inner cannula 130 can alternately comprise a solid rod orobturator which is dimensioned to be received within shaft 112 to openpetals 114.

As can be seen in FIG. 13, a notch 118 is found between adjacent petals114 where petals 114 are mounted to the distal end 113 of cannula shaft112. Notches 118 operate to facilitate breakage of seals 115 byproviding a stress relief region at the base of breakable seals 115.

In an alternate design, as shown in FIGS. 18 and 19, distal tip 113comprises truncated petals 114 a which, when sealed together by way ofbreakable seals 115, meet at their distal end to define a small opening117 at distal tip 113 of cannula shaft 112. In this design, an obturator120 a is slidably received within cannula shaft 112. Obturator 120 a hasa narrow distal end 113 a which protrudes through opening 117.Electrodes 119 a, 119 b, 119 c, 119 d, 119 e and 119 f are disposedradially about the narrow distal end 113 a of obturator 120 a,functioning similar to the probe design shown in FIG. 6.

In this alternate design of FIGS. 18 and 19, nerve surveillance andblood vessel cauterization functions as described above and as performedby electrodes 116 on petals 114 are instead performed by electrodes 119on obturator 120 a. In this aspect of the invention, petals 114 a aretruncated and obturator 120 a protrudes therethrough.

In another alternate embodiment, a peel back cannula having anexpandable tip is provided. Referring to FIG. 20, cannula 150 isprovided. Cannula 150 has a tapered narrow distal end 152 and a tearaway line 153 which is formed in the preferred polymeric material ofcannula 150. Tear away line 153 will split under tension as will beexplained. Cannula 150 may also comprise electrodes 151 which perform asimilar function to the electrodes 116 described herein. Electrodes 151can be disposed axially along the length of cannula 150, or radiallyaround the distal end of cannula 150, or some combination thereof.

An advantage of being disposed axially along the cannula is thatelectrodes 151 will be able to sense the position of a nerve relative tothe cannula in an axial dimension. Similarly, an advantage of beingdisposed radially around the cannula is that the electrodes will be ableto sense the position of a nerve relative to the cannula in a radialdimension. It is to be understood that all embodiments of the presentinvention comprise the concept of nerve surveillance electrodes disposedboth radially around and axially along the nerve surveillance cannula orobturator, and that the radial electrode placement shown in the designof FIGS. 7, 8 and 11 to 19, and the axial electrode placement shown inthe design of FIGS. 20 to 23 is not limiting.

In a preferred method of operation, cannula 150 is advanced such thatits tapered end 152 is adjacent nerve 160 as is seen in FIG. 22. Anobturator 155 is positioned within cannula 150. Obturator 155 providesstructural support for the cannula as it is being inserted or as it ismoving a nerve. Obturator 155 provides structural support for thecannula as it is being inserted or as it is moving a nerve. Obturator155 is thereafter removable such that cannula 150 operates as an openpassageway as will be explained.

A narrow inner cannula 157 may also be provided. Cannula 157 is receivedaround obturator 155 and within cannula 150. When the operator hasdetermined it is safe and desirable to open cannula 150, inner cannula157 is advanced to the position shown in FIGS. 23 and 24. Specifically,inner cannula 157 pushes against the tapered end 152 of cannula 150causing cannula 150 to split open along tear away line 153. Accordingly,inner cannula 157 can be used to provide a cannulated passageway whenobturator 157 has been withdrawn therefrom. Alternatively, inner cannula157 can be replaced by suitably dimensioned obturator for openingcannula 150 along tear away line 153.

Tear away line 153 may be formed by scribing the polymeric materialforming cannula 150. Tear away line 153 preferably runs some distancealong opposite sides of the open end 152 of cannula 150. Alternatively,tear away line 153 can be disposed along the top and bottom of cannula150 as shown.

FIG. 25 is a side view of a curved petal design of the present inventionin a closed position with cannula 220 having outwardly curved petals 212at distal end 215. A nerve 230 is disposed adjacent the ends of closedpetals 212 as shown. Petals 212 are then opened, using methods describedherein, as shown in FIG. 26. The opening of petals 212 causes nerve 230to be generally displaced upward away from an operative site which maypreferably comprise a patient's intervertebral disk 240.

As shown in FIG. 27, an elastomer 250 can be wrapped around the petals212 such that nerves are not pinched in gaps 213 between the adjacentpetals either when the petals are first opened or when the petals areclosed during the removal of the cannula from the patient. It is to beappreciated that elastomer 250 could also be wrapped around the ends ofany of the straight petal designs shown in FIGS. 11 to 19.

The operative site or target site may comprise a patient'sintervertebral disk 240 when the present invention is used in minimallyinvasive spinal surgery. It is to be understood, however, that thepresent expandable tip cannula can be used in all manner of minimallyinvasive surgery and is especially useful for approaching any targetsite having sensitive nerves adjacent thereto since the presentinvention is specifically adapted to gently push the nerve out of theway as the petals are opened, thereby providing a cannulated accessportal for the insertion and removal of various surgical devices throughcannula 220.

FIG. 28 shows an alternate design of the distal end 302 of a nervesurveillance cannula 300. Cannula 300 has a plurality of expandingpetals 314, with each petal 314 comprising an electrode 316 adapted fornerve surveillance or blood vessel cauterization as described above. Inthis aspect of the invention, an obturator 310 protrudes through anopening between petals 314, as shown. As can be seen, obturator 310 maypreferably be tapered to a narrow distal end 302, which assists ineasing cannula 300 through the patient's facia and para-spinalmusculature and into the patient's intervertebral space. In addition,distal end 302 of obturator 310 can be shaped to latch against the endsof petals 314, as shown, thereby assisting in holding together petals314 as cannula 300 is advanced.

Preferably, obturator 310 further comprises a centrally disposedelectrode 320. Electrode 320, being axially displaced from electrodes316 is adapted to sense the position of a nerve in the axial directionas probe 300 approaches the nerve. Subsequent to placement at thepatient's intervertebral space, an internal cannula 315 can be advanceddistally to open petals 314 with obturator 310 being advanced slightlyto first un-latch the distal ends of petals 314 and then withdrawn fromcannula 300, providing a cannulated access to the patient'sintervertebral space.

FIG. 29 through 33 show an alternative nerve surveillance cannula andprobe system 400, comprising a cannula 402 having a plurality ofradially outwardly extending petals 404. An internal obturator 500 isreceived within cannula 402. Obturator 500 has an electrode 502 disposedat its distal end as shown in FIG. 30. Electrode 502 can also be seen atdistal end of cannula 402 in FIG. 29. Electrode 502 operates tostimulate and thereby, depolarize a nerve as cannula 402 is advancedtowards the patient's intervertebral space. FIG. 29 shows cannula 402with petals 404 closed around electrode 502 as the cannula is advanced.

FIG. 30 shows an inner cannula 550 which is advanced through cannula 402to open petals 404 as shown. Inner cannula 550 preferably comprises anelectrode 510 which is disposed around the distal end of the cannula, asshown. After inner cannula 550 has opened petals 404, as shown,electrode 502 is turned off and obturator 500 is removed from innercannula 550 as is shown in FIG. 31. Electrode 510 remains turned on suchthat it is adapted to detect whether a nerve is positioned close toentering within cannula 550, or whether a surgical instrument advancedthrough cannula 550 would contact a nerve proximal electrode 510.

As is shown in FIG. 32, obturator 500 can thereafter be advanced throughcannula 550 to bluntly divide and dilate the annulus of a disc. In thisaspect of the invention, electrode 502 is turned off as the annulus isdivided and dilated. Annular electrode 510 may preferably be turned onduring this procedure to sense the presence of nerves adjacent thedistal end of cannula 550.

As is seen in FIG. 33, after the annulus has been divided and dilated,obturator 500 can be withdrawn from cannula 550 with cannula 550advanced distally into the hole cut into the annulus. As such, a safecannulated access way into the annulus or other region of the patient'sbody is provided.

What is claimed is:
 1. A method of performing spine surgery, comprising:advancing a stimulation instrument and an expandable structure along apath towards a spinal target site, wherein the expandable structureincludes a passageway extending from a proximal end to a distal end, thestimulation instrument fitting within the passageway of the expandablestructure; delivering a stimulation signal from a stimulation electrodedisposed proximate a distal end of the stimulation instrument while thestimulation instrument is positioned along the path to detect thepresence of nerves adjacent the stimulation instrument; manipulating theexpandable structure to increase a circumference of the expandablestructure from a first circumference to a larger second circumference;advancing an access instrument over the expandable structure to thesurgical target site, the access instrument having a second passagewayextending from a proximal end to a distal end, the second passagewayhaving a third circumference fitting around the second circumference ofthe expandable structure; removing the stimulation instrument and theexpandable structure from the second passageway after the accessinstrument has been advanced to the spinal target site; and introducingan implant into the spinal target site through the access instrument. 2.The method of claim 1, wherein the stimulation electrode is one of aplurality of stimulation electrodes radially disposed around the distalend of the stimulation instrument.
 3. The method of claim 2, wherein thestimulation signal is delivered from each of the plurality ofstimulation electrodes in turn to detect the presence of the nerves in aradial direction relative to a central axis of the stimulationinstrument.
 4. The method of claim 1, wherein the step of introducingthe implant includes using at least one of a bone decorticator, acamera, an articulating forcep and an intervertebral positioning system.5. The method of claim 1, wherein the access instrument is a cannula. 6.The method of claim 1, wherein the expandable structure is a mesh. 7.The method of claim 6, wherein the mesh expands from the firstcircumference to the second circumference by shortening the distancebetween the proximal end and the distal end of the mesh.